336
John D. GAGE
rate in oxygen demand, driven by the seasonal changes
in organic flux to the bottom, has been detected at the
abyssal station, Station ‘M’ off California (K.L. Smith
and Baldwin, 1984b), the oxygen consumption of the
sediment community being higher in early summer
than in late autumn and winter. Later time-series
data from the Californian margin out to the central
North Pacific (K.L. Smith, 1987, 1992; K.L. Smith
et al., 1994), have confirmed a pattern of variation
in oxygen consumption consisting of up to fourfold
seasonal increase associated with the peak in particle
flux. However, demonstration of direct coupling to
seasonally varying particulate flux from the surface
has proved more elusive elsewhere. In the abyssal
Northeast Atlantic at the German BIOTRANS site
a seasonal increase in sediment community oxygen
consumption (measured in situ using a benthic lander)
was observed, with a doubling in consumption in
July and August compared to April (Pfannkuche,
1992). But no such seasonality was detected in either
the Porcupine Abyssal Plain at the BENGAL site
(Witbaard et al., 2000), the bathyal Porcupine Seabight
(Lampitt et al., 1995), or nearby on the Goban Spur
(Lohse et al., 1998), or in the deep Sargasso Sea,
southeast of Bermuda (Sayles et al., 1994), despite
large variability in particle flux measured at the
three sites. However, pore-water profiling of retrieved
cores showed a seasonal pattern even if this was
absent in concurrent in situ measurements of oxygen
consumption by the sediment community (Witbaard
et al., 2000). Although the reason for this is still
unclear, and may be artifactual, the lack of the seasonal
signal observed elsewhere has been related to low
nutritional quality in particles (Sayles et al., 1994).
Several other studies have explicitly addressed the
response of the small size classes of the deep-sea
benthic community to phytodetrital mass accumulations (reviewed by Gooday and Turley, 1990). In the
studies mentioned earlier at the German BIOTRANS
site, measurements of various biochemical parameters
and of sediment community oxygen consumption were
taken at different times of the year, along with concurrent measurement of chlorophyll-a and of chloroplastic
pigment equivalents (which include phaeopigments),
both being a measure of reactive phytodetrital material.
The close relationships between them indicate a highly
geared response of the abyssal benthic community
to sedimentation events, with transient increase in
metabolic activity followed by increase in the biomass
of small size groups (Pfannkuche, 1992, 1993). Yearto-year changes in detrital flux also might be reflected
in the response by this size-class. Pfannkuche et al.
(1999) found that the unusual pattern of early sedimentation peaks in March, followed by smaller, transient
ones from June to August, at the BIOTRANS site in
1992 was reflected in various sediment parameters.
The coupling was so close that it could be said that
interannual variability in production in the surface
water is closely mirrored in deep-sea benthic processes
(Fig. 11.11).
Using the same approach, similarly tightly geared
coupling of organic flux to the community in the small
size class was detected on the adjacent continental
margin off southern Ireland. Here, twin sharp peaks
in deposition of chloroplastic pigment and response of
transiently increased enzymic activity and biomass in
the small size-class could be detected on the upper
slope, one in mid-spring and the other in late summer
(Pfannkuche and Soltwedel, 1998). This contrasts with
the flatter summer-time deposition and response peak
observed on the continental rise and abyssal plain.
Furthermore, Graf (1989), using incubation on
shipboard of recompressed sediment cores taken in the
bathyal Norwegian Sea, was able to measure higher
rates in oxygen consumption in cores taken just after a
detrital pulse to the seabed than in those taken before
it occurred.
In the Pacific, Drazen et al. (1998) reported that
protozoan densities and biomass increased significantly
over a 4-week period following phytodetrital input,
showing that these organisms can respond to organicmatter inputs within a time scale as short as weeks.
These data help to explain the seasonal variability measured above. For example, although microbial biomass
in phytodetritus was similar to that in superficial
sediment, whether overlain by phytodetritus or not,
there were many more dividing cells and larger mean
cell volumes within the floc. Lochte and Turley (1988)
and Thiel et al. (1988/89) found more bacteria in the
sediment below the phytodetritus, and a subsurface
peak at depths between 4 and 6 cm, probably resulting
from the rapid incorporation of the labile organics
into the sediment by macrofauna such as depositfeeding sipunculans (see below). Another approach
has addressed benthopelagic coupling by tracking
biotransformation of radio-labelled dissolved organic
substrates in situ in enclosed areas of sediment; in this
case, at a depth of 2000 m in the Northeast Atlantic,
rates of uptake, presumably microbial, measured in
John D. GAGE
rate in oxygen demand, driven by the seasonal changes
in organic flux to the bottom, has been detected at the
abyssal station, Station ‘M’ off California (K.L. Smith
and Baldwin, 1984b), the oxygen consumption of the
sediment community being higher in early summer
than in late autumn and winter. Later time-series
data from the Californian margin out to the central
North Pacific (K.L. Smith, 1987, 1992; K.L. Smith
et al., 1994), have confirmed a pattern of variation
in oxygen consumption consisting of up to fourfold
seasonal increase associated with the peak in particle
flux. However, demonstration of direct coupling to
seasonally varying particulate flux from the surface
has proved more elusive elsewhere. In the abyssal
Northeast Atlantic at the German BIOTRANS site
a seasonal increase in sediment community oxygen
consumption (measured in situ using a benthic lander)
was observed, with a doubling in consumption in
July and August compared to April (Pfannkuche,
1992). But no such seasonality was detected in either
the Porcupine Abyssal Plain at the BENGAL site
(Witbaard et al., 2000), the bathyal Porcupine Seabight
(Lampitt et al., 1995), or nearby on the Goban Spur
(Lohse et al., 1998), or in the deep Sargasso Sea,
southeast of Bermuda (Sayles et al., 1994), despite
large variability in particle flux measured at the
three sites. However, pore-water profiling of retrieved
cores showed a seasonal pattern even if this was
absent in concurrent in situ measurements of oxygen
consumption by the sediment community (Witbaard
et al., 2000). Although the reason for this is still
unclear, and may be artifactual, the lack of the seasonal
signal observed elsewhere has been related to low
nutritional quality in particles (Sayles et al., 1994).
Several other studies have explicitly addressed the
response of the small size classes of the deep-sea
benthic community to phytodetrital mass accumulations (reviewed by Gooday and Turley, 1990). In the
studies mentioned earlier at the German BIOTRANS
site, measurements of various biochemical parameters
and of sediment community oxygen consumption were
taken at different times of the year, along with concurrent measurement of chlorophyll-a and of chloroplastic
pigment equivalents (which include phaeopigments),
both being a measure of reactive phytodetrital material.
The close relationships between them indicate a highly
geared response of the abyssal benthic community
to sedimentation events, with transient increase in
metabolic activity followed by increase in the biomass
of small size groups (Pfannkuche, 1992, 1993). Yearto-year changes in detrital flux also might be reflected
in the response by this size-class. Pfannkuche et al.
(1999) found that the unusual pattern of early sedimentation peaks in March, followed by smaller, transient
ones from June to August, at the BIOTRANS site in
1992 was reflected in various sediment parameters.
The coupling was so close that it could be said that
interannual variability in production in the surface
water is closely mirrored in deep-sea benthic processes
(Fig. 11.11).
Using the same approach, similarly tightly geared
coupling of organic flux to the community in the small
size class was detected on the adjacent continental
margin off southern Ireland. Here, twin sharp peaks
in deposition of chloroplastic pigment and response of
transiently increased enzymic activity and biomass in
the small size-class could be detected on the upper
slope, one in mid-spring and the other in late summer
(Pfannkuche and Soltwedel, 1998). This contrasts with
the flatter summer-time deposition and response peak
observed on the continental rise and abyssal plain.
Furthermore, Graf (1989), using incubation on
shipboard of recompressed sediment cores taken in the
bathyal Norwegian Sea, was able to measure higher
rates in oxygen consumption in cores taken just after a
detrital pulse to the seabed than in those taken before
it occurred.
In the Pacific, Drazen et al. (1998) reported that
protozoan densities and biomass increased significantly
over a 4-week period following phytodetrital input,
showing that these organisms can respond to organicmatter inputs within a time scale as short as weeks.
These data help to explain the seasonal variability measured above. For example, although microbial biomass
in phytodetritus was similar to that in superficial
sediment, whether overlain by phytodetritus or not,
there were many more dividing cells and larger mean
cell volumes within the floc. Lochte and Turley (1988)
and Thiel et al. (1988/89) found more bacteria in the
sediment below the phytodetritus, and a subsurface
peak at depths between 4 and 6 cm, probably resulting
from the rapid incorporation of the labile organics
into the sediment by macrofauna such as depositfeeding sipunculans (see below). Another approach
has addressed benthopelagic coupling by tracking
biotransformation of radio-labelled dissolved organic
substrates in situ in enclosed areas of sediment; in this
case, at a depth of 2000 m in the Northeast Atlantic,
rates of uptake, presumably microbial, measured in